The Sensex at the Bombay Stock Exchange on Monday gained 56 points, or 0.3 percent, to 17,151 on a slight easing of inflation, hopes of a rate cut by the Reserve Bank in its credit policy announcement, tomorrow, and rising European markets. The Nifty at the National Stock Exchange rose 19 points, or 0.4 percent, to 5,226.But stock markets in Japan, China, Hong Kong, and South Korea declined between 0.1 percent and 17 percent.